# Physics - electrons, waves and photons

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 Author: jpopat ID: 213447 Filename: Physics - electrons, waves and photons Updated: 2013-04-14 15:53:54 Tags: Physics electrons waves photons Folders: Description: Physics - electrons, waves and photons Show Answers:

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1. Ampere
A current or rate of flow of charge of one coulomb per second
2. Charge
A fundamental property of matter and may be positive or negative
3. Coulomb
A unit of charge produced when a current of 1A flows for 1s
4. Kilowatt hour
A unit of energy produced when a device rated at a power of 1kW is used for 1 hour (equal to 3.6 MJ)
5. Kirchhoff's 1st Law
The sum of currents entering a junction is equal to the sum of currents leaving a junction (conservation of charge)
6. Kirchhoff's 2nd Law
The sum of emf around a loop is equal to the sum pd round the loop (conservation of energy)
7. Mean drift velocity
The average velocity that a charged particle attains due to an electric field
8. Terminal pd
The voltage across the ends of a battery and is equal to the emf-lost volts
9. Ohm
The resistance of a conductor through which a current of 1A is flowing when the pd across it is 1v
10. Ohm's Law
The current though a metallic conductor is directly proportional to the potential difference across it provided there is no change in the physical conditions (eg temperature) of the conductor
11. The resistance of an LDR
As light intensity increases, resistance of the LDR decreases
12. Photon
A quantum of energy of electromagnetic radiation (E=hf)
13. Resistivity
(Resistance x cross sectional area) / length
14. Planck's Law
E=hf
15. Resistance
Pd across conductor / current across conductor
16. Potential difference (pd)
Between two points in a circuit is the amount of energy in joules changed into other forms per coulomb of charge that passes from one point to another
17. Power
Rate of conversion of energy in watts (= joules per second)
18. Volt
One joule of energy per coulomb of charge
19. Work function
The minimum photon energy needed to eject a photoelectron from a metal
20. Current
The rate of flow of charge
21. EMF
Electrical energy transferred per unit charge as the charge passes through a source
22. Internal resistance
Is responsible for energy lost in a cell when a current flows though it
23. Threshold frequency
The minimum frequency of incident radiation needed to release photoelectrons
24. Coherence
Constant phase difference
25. Laws of reflection
• 1. The reflected ray, the incident ray and the normal are coplanar
• 2. The angle of reflection is equal to the angle of incidence
26. Malus' Law
I =
27. UV - A
Causes sun tan
28. UV - B
Causes sunburn and skin cancer
29. Wavelength of visible light
• m
• m
30. Intensity
• Intensity = power / surface area
• Intensity  amplitude2
31. For a maximum the path difference...
Is equal to a whole number of wavelengths
32. For a minimum the path difference...
Is equal to an odd number of half wavelengths
33. Transverse wave
The direction of particle oscillation is perpendicular to the direction of energy travel
34. Longitudinal wave
The direction of particle oscillation is parallel to the direction of energy travel
35. Wavelength
The distance between two consecutive points which are in step
36. Displacement
How far and in which direction each particle is from it's central undisturbed position
37. Amplitude
The maximum displacement that the particles obtain from their central undisturbed position
38. Frequency
The number of complete cycles of oscillation performed per second
39. Period
The time taken to perform one complete cycle of oscillation
40. Relationship between frequency and period
f = 1/T
41. Wave speed
V = f
42. In phase
Two waves are said to be exactly in phase if all the crests of one exactly align with the crests of the other
43. Out of phase (180•)
If the crests of one wave line up with the troughs of another
44. Polarisation
A property of transverse waves where all the oscillations are in the same plane
45. Pitch
Of a sound depends on frequency
46. Loudness
Of sound is determined by the amplitude of the vibrations
47. The principle of superposition
The vector addition of the displacements of two or more waves that meet

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